Case 3: Neonate with Sudden Onset of Hypotonia on the Second Day After Birth

Abstract

A 2-day-old 3-kg female term neonate is born in a normal vaginal delivery with Apgar scores of 8, 8, and 9 at 1, 5, and 10 minutes, respectively. During morning rounds, she is noted to have a weak cry. Antenatal and natal history findings are normal. Detailed neurologic examination shows a fully conscious neonate with decreased shoulder tone and head lag. Neonatal reflexes are also diminished, with a weak cry, poor swallowing, and poor sucking reflex. There are no clinical features of respiratory distress or respiratory failure, shock, seizure, or altered sensorium. The neonate is evaluated with a sepsis screen, serum glucose, serum calcium, serum electrolytes, and serum magnesium for neonatal sepsis or metabolic derangements. Laboratory investigation shows normal sepsis screen and metabolic evaluation (total white blood cell count of 13,000/μL [13×109/L], C-reactive protein level of 0.01 mg/L [0.10 nmol/L], serum glucose of 89 mg/dL [4.9 mmol/L], total serum calcium of 8.4 mg/dL [2.1 mmol/L], ionized calcium of 4.6 mg/dL [1.1 mmol/L], serum magnesium of 1.3 mEq/L [0.65 mmol/L], serum sodium of 138 mEq/L [138 mmol/L], and serum potassium of 4.6 mEq/L [4.6 mmol/L]). Head neurosonography to rule out any bleeding or malformations has normal findings but neonatal hypotonia persists. At this time, one investigation clinches the diagnosis. In a neonate with sudden onset of hypotonia, the initial differential diagnosis includes neonatal sepsis; metabolic derangements such as hypermagnesemia, hypocalcemia, and hypokalemia; antibiotic toxicity due to aminoglycosides; botulism; and cerebral malformations or bleeding. The neonate was evaluated for metabolic causes and neonatal sepsis, and the investigation showed normal sepsis screen and metabolic profile, thus ruling out these causes. The infant had no history of receiving antibiotics and she was exclusively breastfed, thus ruling out elevated levels of aminoglycosides or …